Brigham and Women's Hospital(PITTSBURGH) -- The husband of a Pennsylvania doctor who died with "toxic levels of cyanide" in her system is being investigated as a person of interest, his attorney told ABC News Friday.

Autumn Klein, 41, collapsed at her home in Pittsburgh's Oakland neighborhood and later died on April 20 at UPMC Presbyterian Hospital, where she was chief of the division of women's neurology and an assistant professor of neurology, obstetrics and gynecology.

Her husband, Dr. Robert Ferrante, 64, is a professor of neurological surgery at University of Pittsburgh. The couple has a 6-year-old daughter named Cianna.

"There's no question he's a person of interest and that's really all I can go into now," William Difenderfer, Ferrante's attorney, told ABCNews.

"He's under investigation, as any case like this would be, and that's about all we know from the standpoint of the government and he has retained me and we have some experts on board too," Difenderfer said. "We're looking into things as well."

He "adamantly" denied that Ferrante was responsible for or in any way was involved in his wife's death.

"We're going to anxiously defend the case at this point," he said. "I don't want to even get in on a debate with this case now until we see what the commonwealth does."

Difenderfer said he was not aware of police talking to his client recently.

When asked about reports that Ferrante may have purchased cyanide with a university credit card, Difenderfer said, "I can't confirm or deny that. I don't know."

A source briefed on the case told ABC News that investigators believe Ferrante ordered cyanide prior to his wife's death. Detectives have not questioned the doctor about that, but are aware that his attorney has told others that the chemical was used in Ferrante's research.

Ferrante is currently the only person under suspicion in connection with the death of his wife.

"No one else is being looked at," the source said, insisting that that could still change if new leads are developed.

Pittsburgh police again declined comment when contacted by ABC News on Friday.

Authorities have said that Klein's death is being investigated as a possible homicide and a possible suicide.

The FBI is working to assist the Pittsburgh police in the investigation. Earlier this month, police executed a search warrant to search the couple's home.

Investigators removed three vacuum cleaners, a computer tower, and towed the couple's cars.

Warrants were executed for "PITT and/or UPMC," where Ferrante and Klein worked, respectively, according to authorities.

Veteran forensic pathologist Cyril Wecht told ABC News recently that he has been retained to consult in the investigation of Klein's death, but did not say who hired him.